What distinguishes tenascin from fibronectin?

Tenascin and fibronectin are two major extracellular matrix glycoproteins. They both consist of large disulfide-linked subunits composed of multiple structural domains. More than half of each molecule consists of so-called fibronectin type III repeats, but the other domains differ. Fibronectin is a dimer, whereas tenascin is a hexamer. Often fibronectin and tenascin are colocalized in tissues, but the occurrence of tenascin is much more restricted when compared with fibronectin. Tenascin is transiently expressed in many developing organs such as connective tissues, the mesenchyme of epithelial organs, and also the central and peripheral nervous systems, and it reappears in the stroma of many tumors. The distinctive and highly regulated expression of tenascin has provoked interest in trying to identify possible functions of tenascin in cell-cell and cell-substratum adhesion, cell migration, growth, and cell differentiation during morphogenesis.